There's not; your eyes see the vague white lines formed by the lighter boxes, but when they're in your peripheral vision your brain is filling in the missing information, and because they're so close in location, colour, and thickness to the straight lines, your brain conflates the two. This results in exaggerating the white lines so you're more aware of them than when you're looking straight at them and can see the outlines of the white boxes clearly, and the white and green lines seem to blend when they're both in your peripheral vision.